Quantitative cytochemistry and quantitative stereology will be used to examine enzymic and ultrastructural characteristics of follicles destined to ovulate in rats. Among the enzymes that will be studied are delta 5-3beta-hydroxysteroid dehydrogenase, an enzyme typically involved with steroidogenesis, and glucose-6-phosphate dehydrogenase and cytochrome P-450, enzyme complexes involved with both steroidogenesis and other biosynthetic functions. Two lysosomal enzymes, acid phosphatase and napthylamidase will be studied; acid phosphatase to localize organelles which display lysosomal activity and napthylamidase to measure lysosomal membrane permeability. After the enzymic, morphologic and ultrastructural characteristics of the ovulable type of follicle are established in a follicle in proestrous, the development of these characteristics will be traced through the estrous cycle in follicles that are destined to ovulate. It is well known that many conditions associated with female infertility can be associated with the formation of an inadequate corpora lutea. Since it is the granulosa cells from the ovulable type of follicle that will form the new corpora lutea it is vital that these cells be carefully studied.